1. Field of the Invention
The present invention relates to a method of manufacturing an electrode for a lithium secondary cell, and more particularly, it relates to a method of manufacturing an electrode for a lithium secondary cell by forming active material layers on both surfaces of a collector.
2. Description of the Background Art
As to a lithium secondary cell recently subjected to flourishing research and development, cell characteristics such as the charge and discharge voltages, the operating cycle life and the storage characteristics remarkably depend on the employed electrodes. Therefore, active materials employed for the electrodes are improved for improving and upgrading the cell characteristics.
It is known that a cell having high energy density per weight and per volume is obtained when employing lithium metal as a negative active material. In this case, lithium is deposited by charging and dissolved by discharging on a negative electrode. When the cell is repetitively charged and discharged, lithium is repetitively deposited and dissolved on the negative electrode. Thus, lithium is disadvantageously dendritically deposited on the negative electrode. Consequently, internal shorting is disadvantageously caused.
To this end, there has been proposed a lithium secondary cell suppressing the aforementioned dendritic deposition of lithium by employing aluminum, silicon or tin electrochemically alloyed with lithium in charging as a negative electrode active material, as reported in Solid State Ionics, 113-115, p. 57 (1998), for example. Among these materials, silicon having particularly large theoretical capacity is a prospective material as the active material for the negative electrode of a cell exhibiting high capacity.
The assignee of the present invention has proposed an electrode for a lithium secondary cell having a negative electrode active material layer consisting of a microcrystalline silicon layer or an amorphous silicon layer formed on a collector by CVD or sputtering in International Laying-Open No. WO01/29912. The assignee has also proposed an electrode for a lithium secondary cell having active material layers consisting of microcrystalline silicon layers or amorphous silicon layers formed on both surfaces of a plate collector by plasma CVD in International Laying-Open No. WO01/29918.
In the aforementioned technique proposed by the assignee, active material layers each consisting of a plurality of layers may be formed on both surfaces of a collector when the microcrystalline silicon layers or the amorphous silicon layers are formed on both surfaces of the collector by plasma CVD or the like.
When a first active material layer consisting of a plurality of layers is continuously formed on a first surface of the collector for thereafter continuously forming a second active material layer consisting of a plurality of layers on a second surface of the collector in this case, the first active material layer formed in advance is re-heated in formation of the second active material layer. Therefore, the component of the collector disadvantageously excessively diffuses into the first active material layer formed in advance. Thus, it follows that the component of the collector diffuses into the first and second active material layers formed on the first and second surfaces of the collector respectively in different states, and hence it is disadvantageously difficult to control the diffusion states in the first and second active material layers formed on the first and second surfaces of the collector respectively.
In general, therefore, it is difficult to obtain electrodes for a lithium secondary cell having high charge/discharge capacity and excellent operating cycle characteristics.